Intermediary low viscosity bonding resins were introduced for application to etched enamel surfaces prior to the placement of conventional composite restorative resins because it was reasoned that low viscosity bonding resins would penetrate deeper into the etched enamel surfaces and thus ensure intimate interfacial contact between the restorative resin and enamel. The results of recent in vitro studies carried out in our laboratory indicated that the use of a low viscosity bonding resin did not improve the bond strength of a conventional composite resin to etched enamel, did not enhance the penetration of the resin into the microspaces in the etched enamel and did not significantly reduce microleakage. The purpose of this clinical study is to evaluate the effect of a low viscosity bonding resin on the clinical performance of conventional composite resin restorations. Subjects with at least two Class III or V lesions located on the maxillary anterior teeth were selected to participate in the study. The prepared cavity preparation in each subject designated through random selection to receive a low viscosity bonding agent at the etched enamel surface was restored with a conventional composite restorative resin while the paired preparation was restored without the prior application of the bonding resin. Pre- and postoperative photographs were taken and at the first and 18- month recall impressions were taken of the restorations and replicas made to evaluate marginal adaptation of the restorations by SEM. Anatomic form of the restorations, the presence of secondary caries, color match, cavosurface marginal discoloration, and marginal adaptation were determined clinically after each visit. Sixty-five paired restorations have been placed and evaluated 18 months after placement. No significant differences in the criteria evaluated have been observed. It is proposed to extend this study to further evaluate the clinical performance of the restorations three years after placement. More sensitive evaluation criteria will be used to evaluate the restorations.